"By far, the bulk of age limits are around 18 and 20, but there are a considerable number of countries that have 21," Rekve said.

"So you have everything from a total ban, where nobody can buy or sell, to an age range of limits from 13 to 25, and then there are some countries that don't have any age limits whatsoever. It's legal to sell to anyone," he said.

Yet in recent years, more attention has turned to how much alcohol young people are drinking, not necessarily the age at which drinking starts.

Where teen drinking is highest and lowest

Binge or heavy episodic drinking can be measured as consuming at least 60 grams or more of pure alcohol on at least one occasion in the past 30 days. Worldwide, about 16% of drinkers 15 and older engage in heavy episodic drinking, according to WHO.

"Ten grams of alcohol is a standard drink, which is approximately almost a bottle of beer, a glass of wine or a standard drink of spirits," Rekve said. In the United States, the Centers for Disease Control and Prevention defines a standard drink as equal to 14 grams of pure alcohol.

No other countries had more than half of teens in that age group report heavy episodic drinking in the past 30 days.

Countries where no 15- to 19-year-olds reported heavy episodic drinking in the past 30 days were Mauritania, Afghanistan, Kuwait, Libya, Pakistan, Somalia, Syria and Yemen.

"Europe usually is really high, both for the adult population and for 15- to 19-year-olds," Rekve said. More than one-fifth of the European population 15 and older has reported heavy episodic drinking at least once a week, according to WHO.

He added, however, that many European countries have recently seen a drop in alcohol use that mirrors the number of adolescents abstaining from drinking altogether.

One study, published in the journal BMC Public Health in October, found that 29% of 16- to 24-year-olds in England were non-drinkers in 2015, up from 18% in 2005.

A WHO report published in September found that, across 15 European countries and regions, more than 1 in 5 15-year-old girls reported weekly drinking in 2002, with the highest prevalence in England, Scotland, Malta and Denmark. But by 2014, only Malta had a prevalence greater than 20%.

Among 15-year-old boys, more than 1 in 5 reported weekly drinking across 24 European countries and regions, with the highest prevalence in Malta, Denmark, England, and Wales. But by 2014, only nine countries and regions had a prevalence greater than 20%, with the highest prevalence in Croatia, Malta, and Italy, according to the report.

In the United States, rates of binge drinking among teenagers also have been on the decline.

Those percentages were down from 2013, when it was reported by 10.2%, 25.7% and 39.2% of eighth-, 10th- and 12th-graders, respectively, according to the report.

Overall, the percentage of teenagers in America who reported ever using alcohol dropped as much as 58% from its peak in 1994.

"Even parents have a tolerance to alcohol, and in many instances, they maybe even provide the alcohol for parties that they are holding in their house, with the sense that, what harm is there to let teenagers drink when they are home?" said Dr. Nora Volkow, director of the National Institute on Drug Abuse, which funded the report.

"So we have a culture about drinking that is very accepted but that is slowly changing. I think changes in attitudes are in part responsible about why we're seeing the decreases," she said.

How heavy drinking can affect young people's health

Studies have varied, but some researchers say no amount of alcohol is good for your health, and binge drinking can damage the body and brain, especially in a young person. Evidence suggests that heavy exposure to alcohol can be tied to brain impairment and cognitive deficits, including memory problems.

In general, excessive alcohol consumption ranks as the leading risk factor for an early death or disability in 15- to 49-year-olds, Rekve said.

In other words, of all the factors that could raise your risk for death or disability -- such as tobacco use or physical inactivity -- too much drinking was the leading risk factor globally among that age group in 2016, according to a study published in The Lancet in August.

The study, based on an analysis of data for 195 countries and territories, found that alcohol use was associated with 3.8% of deaths in girls and women in that age group and 12.2% of deaths in boys and men in the same age group.

"At the same time, we know that almost 60% of the world's population are not currently drinkers who are 15 years and older. That means that there might be a lot of changes in the future that we need to be aware of," Rekve said, referencing how in 2016, 57% of men and women worldwide reported abstaining from drinking alcohol in the past 12 months.

In September, WHO launched an initiative called SAFER in an effort to help governments around the world reduce the harmful impacts of excessive alcohol consumption.

The initiative features five strategies: enacting and enforcing policies related to alcohol, advancing and enforcing measures to reduce drunken driving, facilitating access to interventions or treatment for alcohol problems, enforcing restrictions around alcohol advertising and considering alcohol taxation and pricing policies.

As WHO puts it, in many parts of the world, drinking alcoholic beverages is a big part of social gatherings and celebrations -- but moderation remains key.